1. Field of the Invention
The present invention relates to a method for fabricating a semiconductor photonic device, and more particularly, to a method for fabricating an integrated semiconductor photonic device in which an active waveguide and a passive waveguide are combined with each other on a substrate.
2. Description of the Related Art
When fabricating a semiconductor photonic device, a current confinement layer is fabricated generally by a method of forming a p/n/p current confinement layer or a method of forming a current confinement layer of buried ridge strip (BRS) type. Using the method of forming a p/n/p current confinement layer, it is possible to effectively block electric current. However, this method has the disadvantage of there being slight variations in the structure of the resulting semiconductor photonic devices, especially, when a waveguide of a top and bottom dual structure is manufactured by combining a waveguide with a mode-conversion type passive waveguide. That is, this method is disadvantageous regarding reproducibility, whereas the method of forming a BRS type current confinement layer is profitable regarding reproducibility.
FIGS. 1A through 1D are views explaining a method of forming a BRS type current confinement layer, which is disclosed in U.S. Pat. No. 6,025,207. In detail, a buffer layer 11, a guiding layer 12, an intermediate layer 13 and an active layer 14 are sequentially deposited on a substrate 10. Next, as shown in FIG. 1B, the active layer 14 is patterned in the form of a strip, and portions of the intermediate layer 13, which are exposed due to the patterning of the active layer 14, are also etched. Then, referring to FIG. 1C, resumption of epitaxial growth is used to bury the active layer 14 in the p-type clad layer 16, and then a conductive layer 18 is deposited on the p-type clad layer 16. Thereafter, an ion implantation mask 26 is formed on the conductive layer 18, being aligned with respect to the active layer 14. Next, ions are implanted into the p-type clad layer 16 so as to form ion-implanted regions 17a and 17b at the both sides of the active layer 14. As a result, a current confinement layer, which is defined by a channel C, is formed between the ion-implanted regions 17a and 17b. Then, referring to FIG. 1D, the ion implantation mask 26 is removed to form a contact layer 20 on the conductive layer 18.
The method of forming a BRS type current confinement layer is easy to fabricate a photonic device by performing resumption of epitaxial growth only once. Therefore, this method has reproducibility when semiconductor devices are fabricated. However, this method is not proper in fabricating a monolithic integrated semiconductor photonic device that is integrated with a passive waveguide. Specifically, when fabricating the monolithic integrated semiconductor photonic device, it is very important to effectively combine an active layer with a passive waveguide. However, the method of forming a BRS type current confinement layer requires a p-type clad layer basically, which would result in higher optical losses when the active layer is combined with the passive waveguide. Further, an ion implanter, which is very expensive, is required, thereby increasing manufacturing cost therefor.
To solve these problems, A. Labrousse et al. suggested that a passive waveguide be made in the form of a deep ridge and then coupled with a BRS type active layer, disclosed in their thesis entitled xe2x80x9cFirst 20 Gbit/s All Optical Wavelength Conversion with an Integrated Active-Passive Mach/Zehnder Interferometer and Comparison with the Similar All-Active Devicexe2x80x9d which was introduced in OAA 2001, OWA2. However, a deep ridge-type passive waveguide has higher optical losses than a buried waveguide. Also, the structure of a deep-ridge-type passive waveguide is very different from that of a buried active waveguide. For this reason, a monolithic integrated semiconductor photonic device has low coupling coefficient at a portion where the deep-ridge-type passive waveguide is combined with the buried active waveguide.
To solve the above problem, it is an object of the present invention to provide a method of fabricating a monolithic integrated semiconductor photonic device by effectively combining an active waveguide and a passive waveguide with each other, and minimizing a loss of light therein.
To achieve the above object, there is provided a method of fabricating a monolithic integrated semiconductor photonic device that effectively combines an active waveguide and a passive waveguide, and minimizes an optical loss, including: forming an active layer of a strip shape and a passive layer of a strip shape, which is connected directly to the active layer, on a first conductive substrate; forming a non-doped clad layer around the passive layer so as to form a passive waveguide, and a buried ridge strip (BRS) type current confinement layer around the active layer without ion injection; and forming a second conductive current injection layer on the resultant structure having the current confinement layer so as to form an active waveguide coupled to the passive waveguide.
According to the present invention, it is possible to remarkably reduce an optical loss in a passive waveguide by forming a non-doped clad layer around a passive layer. Also, a current confinement layer can be formed around an active layer without implanting ions, so that expensive equipment such as an ion implanter is not required. In addition, the active waveguide can be effectively coupled with the passive waveguide.